Crystal structure changes of LiMn_(0.5)O_2 cathode materials during charge and discharge studied by synchrotron based in situ XRD

摘要

The structural changes of LiMn_(0.5)Ni_(0.5)O_2, used as a cathode material in a lithium half-cell, have been studied during charge-discharge using synchrotron based in situ X-ray diffraction spectroscopy. A phase transition from a hexagonal structure (H1) to another hexagonal structure (H2) was observed during a C/17 charge to 4.7 V. The new H2 unit cell has a shorter "a" axis and a longer "c" axis, as was observed in the LiNiO_2 cathode material during charge. However, the second phase transition that occurs in discharge, the Li_xMn_(0.5)Ni_(0.5)O_2 structure reversibly changed back from H2 to H1. After that, another hexagonal structure H0 with a slightly larger "a" parameter was formed following further discharging. Extended discharge at a voltage near 1V resulted in an amorphous structure.